Methods and apparatuses for transform skip mode information signaling

ABSTRACT

Video processing methods and apparatuses in a video coding system include receiving input video data of a current block in a current picture, determining whether a transform skip mode is enabled for the current picture, signaling or parsing a syntax element associated with a size constraint for enabling the transform skip mode in a SPS referred to by the current picture when the transform skip mode is enabled, determining whether the transform skip mode is applied to the current block when the current block satisfies the size constraint, processing residues of the current block according to the transform skip mode when the transform skip mode is applied to the current block, and encoding or decoding the current block. An enabling flag is signaled in a high-level syntax set or parsed from the high-level syntax set to determine whether the transform skip mode is enabled for the current picture.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention claims priority to U.S. Provisional PatentApplication, Ser. No. 62/938,365, filed on Nov. 21, 2019, entitled“Methods and apparatus for signaling high-level information related totransform skip mode for coding image and video data”, and U.S.Provisional Patent Application, Ser. No. 62/984,821, filed on Mar. 4,2020, entitled “Methods and apparatus for signaling high-levelinformation related to the transform skip mode”. The U.S. ProvisionalPatent applications are hereby incorporated by reference in theirentireties.

FIELD OF THE INVENTION

The present invention relates to video processing methods andapparatuses for encoding or decoding video data in a video encoding ordecoding system. In particular, the present invention relates totransform skip mode information signaling for a video encoding ordecoding system.

BACKGROUND AND RELATED ART

The High-Efficiency Video Coding (HEVC) standard is the latest videocoding standard developed by the Joint Collaborative Team on VideoCoding (JCT-VC) group of video coding experts from ITU-T Study Group.The HEVC standard relies on a block-based coding structure which splitseach video picture into multiple non-overlapped square Coding Tree Units(CTUs). Each individual CTU in a video picture or a slice is processedin a raster scanning order. In the HEVC main profile, the maximum andthe minimum sizes of a CTU are specified by syntax elements signaled ina Sequence Parameter Set (SPS). A coded picture may be represented by acollection of slices, and each slice is composed of an integer number ofCTUs. A Bi-predictive (B) slice may be decoded using intra prediction orinter prediction with at most two motion vectors and reference indicesto predict sample values of each block in the B slice. A Predictive (P)slice is decoded using intra prediction or inter prediction with at mostone motion vector and reference index to predict sample values of eachblock in the P slice. An Intra (I) slice is decoded using intraprediction only.

Each CTU is further recursively partitioned into one or morenon-overlapped Coding Units (CUs) using quadtree (QT) splittingstructure in order to adapt various local characteristics. At eachpartition depth of the QT splitting structure, an N×N block is either asingle leaf CU or split into four smaller blocks with equal sizeN/2×N/2. The CTU with the size M×M pixel samples is the root node of aquadtree coding tree, and the four M/2×M/2 blocks are the child quadtreenodes split from the root node. Each of the four M/2×M/2 blocks maybecome a parent node partitioned by another QT splitting to result infour child nodes with further reduced size by half in each spatialdimension. If a coding tree node is not further split, it is called aleaf CU. The leaf CU size is restricted to be larger than or equal to aminimum allowed CU size, which is also specified in the SPS. An exampleof a recursive quadtree splitting structure for a CTU is illustrated inFIG. 1, where the solid lines indicate CU boundaries in the CTU.

Once the CTUs are partitioned into leaf CUs, each leaf CU is subject tofurther split into one or more Prediction Units (PUs) according to a PUsplitting type for prediction according to the HEVC standard. Unlike therecursive quadtree splitting for CUs, each leaf CU may only be splitonce to form one or more PUs. The PU and associated CU syntax work as abasic representative block for sharing prediction information as thesame prediction process is applied to all pixel samples in the PU. Thespecified prediction process is employed to predict the values of theassociated pixel samples inside the PU. The prediction information isconveyed to the decoder on a PU basis. After obtaining residuesgenerated by the prediction process based on the PU splitting type, theresidues belonging to a leaf CU are partitioned into one or moreTransform Units (TUs) according to a Residual QuadTree (RQT) splittingstructure for transforming the residues into transform coefficients forcompact data representation. The dashed lines in FIG. 1 indicate TUboundaries in the CTU. The TU is a basic representative block forapplying transform and quantization on the residual data or transformcoefficients. A TU is composed of a Transform Block (TB) of luminance(luma) samples of size 8×8, 16×16, or 32×32 or four TBs of luma samplesof size 4×4, and two corresponding TBs of chroma samples in a picturecoded by a 4:2:0 color format. For each TU, a transform matrix havingthe same size as the TU is applied to the residues to generate transformcoefficients, and these transform coefficients are quantized andconveyed to the decoder on a TU basis. FIG. 2 illustrates an example ofa corresponding QT representation for the block partitioning structureas shown in FIG. 1. The solid lines indicate CU boundaries and thedashed lines indicate TU boundaries within the CTU.

The terms Coding Tree Block (CTB), Coding block (CB), Prediction Block(PB), and TB are defined to specify two-dimensional (2-D) sample arrayof one color component associated with the CTU, CU, PU, and TUrespectively. For example, a CTU consists of one luma CTB, two chromaCTBs, and its associated syntax elements. A similar relationship isvalid for CU, PU, and TU. In the HEVC standard, the same quadtreesplitting structure is generally applied to both luma and chromacomponents unless a minimum size for the chroma block is reached.

The Transform Skip (TS) mode is a coding tool that processes a quantizedresidual signal by entropy coding without going through the traditionaltransform operation. Residues of a block coded in the TS mode areencoded directly in a sample domain instead of transforming into afrequency domain. The TS mode is found to be particularly beneficial forscreen content coding especially for regions with sharp edges and simplecolors. The TS mode can be controlled by high level syntax elements, forexample, an enabling flag transform_skip_enabled_flag signaled in aPicture Parameter Set (PPS) is used to indicate whether the TS mode isenabled or disabled, and a syntax element log2_max_transform_skip_block_size_minus2 signaled in the PPS is used tosignal a size constraint for enabling the TS mode. For example, the TSmode is only allowed to be applied to a transform block with a width andheight smaller than or equal to 32 luma samples. In cases of the TS modeenabled for a current picture, a transform block level flagtransform_skip_flag is signaled for each non-empty transform blocksatisfying the size constraint to indicate whether the TS mode isapplied to the non-empty transform block. The size constraint issatisfied when the block width is less than or equal to 1<<(log2_max_transform_block_size_minus2+2). The transform block is coded inthe TS mode when the corresponding transform block level flagtransform_skip_flag is equal to 1; otherwise the regular transformoperation is applied to the transform block. The transform block levelflag transform_skip_flag is inferred to be equal to 0 when this flag isnot coded. Both dependent quantization and sign data hiding are disabledwhen the TS mode is applied to a transform block. Transform blocks codedin the TS mode are processed by a separate parsing process.

BRIEF SUMMARY OF THE INVENTION

Methods and apparatuses of video processing in a video encoding ordecoding system for encoding or decoding video data in video picturescomprise receiving input data associated with a current block in acurrent picture, determining whether a transform skip mode is enabledfor the current block, signaling or parsing a syntax element associatedwith a size constraint for enabling the transform skip mode only whenthe transform skip mode is enabled, and determining whether thetransform skip mode is applied to the current block when the transformskip mode is enabled for the current block and the current blocksatisfies the size constraint for enabling the transform skip mode. Thesyntax element associated with the size constraint for enabling thetransform skip mode is signaled in a Sequence Parameter Set (SPS) orparsed from a SPS, where the SPS is referred to by the current picture.The video processing methods then process residues associated with thecurrent block according to the transform skip mode when the transformskip mode is applied to the current block, or process residues of thecurrent block by a regular transform operation or regular inversetransform operation when the transform skip mode is not applied to thecurrent block, and the video processing methods further encode or decodethe current block in the current picture.

In some embodiments, the step of determining whether a transform skipmode is enabled for the current block includes parsing an enabling flagfor the transform skip mode from a high-level syntax set, and thetransform skip mode is enabled for the current block when the enablingflag is equal to 1. The transform skip mode is disabled for the currentpicture when the enabling flag is equal to 0. The high-level syntax setis one or a combination of the SPS, Picture Parameter Set (PPS), pictureheader, and slice header. In one embodiment, the video processing methodfurther signals or parses a new syntax element in the SPS when theenabling flag is equal to 1. The new syntax element indicates whether aslice level syntax element is present in slice headers referring to theSPS, and the slice level syntax element for a current slice is used todetermine parsing residues of transform skip blocks in the current sliceby a regular residual coding process or transform skip residual codingprocess.

Some embodiments of the video processing method for the video encodingsystem further comprise signaling information related to a minimumallowed Quantization Parameter (QP) value associated with quantizationof residues of transform blocks processed using the transform skip modewhen the transform skip mode is enabled for the current picture. Theinformation related to a minimum allowed QP value is signaled in theSPS. Similarly, some embodiments of the video processing method for thevideo decoding system further comprise parsing information related to aminimum allowed QP value associated with inverse quantization of aquantized residual signal of transform blocks processed using thetransform skip mode when the transform skip mode is enabled for thecurrent picture.

The syntax element associated with a size constraint for enabling thetransform skip mode corresponds to information for deriving a maximumallowed block size for enabling the transform skip mode according tosome embodiments of the present invention. For example, the maximumallowed block size for enabling the transform skip mode relates to anumber of total pixel samples, a width, or a height of a block. In oneembodiment, the maximum allowed block size for enabling the transformskip mode is less than or equal to a maximum allowed transform blocksize or a maximum allowed non-empty transform block size for codingtransform blocks using the regular transform operation. Similarly, themaximum allowed block size for enabling the transform skip mode forchroma transform blocks is less than or equal to a maximum allowedtransform block size or a maximum allowed non-empty transform block sizefor coding the chroma transform blocks using the regular transformoperation.

In some embodiments, the syntax element associated with a sizeconstraint for the transform skip mode signaled in the SPS is for lumatransform blocks, and a size constraint for enabling the transform skipmode for chroma transform blocks is derived from the size constraint forenabling the transform skip mode for the luma transform blocks. Forexample, the size constraint for enabling the transform skip mode forthe chroma transform blocks is set equal to a same value as the sizeconstraint for enabling the transform skip mode for the luma transformblocks. In another example, the size constraint for enabling thetransform skip mode for the chroma transform blocks is derived accordingto the size constraint for enabling the transform skip mode for the lumatransform blocks and variables SubWdithC and SubHeightC indicatingdown-sampling ratios associated with chroma bitplanes in horizontal andvertical dimensions.

In one embodiment, the video processing method further comprisessignaling a second syntax flag in a high-level syntax set or parsing asecond syntax flag from a high-level syntax set when the transform skipmode is enabled for the current block. The second syntax flag is used tocontrol whether one or more syntax elements related to the transformskip mode are present in a lower-level syntax set associated with eachof lower-level video data units referring to the high-level syntax set.For example, the high-level syntax set is the SPS, a PPS, referred to bythe current picture, or a picture header associated with the currentpicture, and the lower-level syntax set is a picture header associatedwith the current picture or a slice header associated with a currentslice in the current picture. In one embodiment, the one or more syntaxelement related to the transform skip mode supposed to present in thelower-level syntax set are set to a default setting when the one or moresyntax element are not signaled in the lower-level syntax set. Forexample, the default setting is derived from related parameters signaledin the high-level syntax set or the default setting is explicitlysignaled by one or more syntax elements in the high-level syntax set.

Aspects of the disclosure further provide an apparatus implemented in avideo encoding or decoding system, and the apparatus receives inputvideo data of a current block in a current picture, determines whether atransform skip mode is enabled for the current block, signals or parsesa syntax element associated with a size constraint for enabling thetransform skip mode in a SPS referred to by the current picture when thetransform skip mode is enabled, determines whether the transform skipmode is applied to the current block when the transform skip mode isenabled and the current block satisfies the size constraint for enablingthe transform skip mode, processes residues associated with the currentblock according to the transform skip mode when the transform skip modeis applied to the current block or processes residues of the currentblock by a regular transform operation or regular inverse transformoperation when the transform skip mode is not applied to the currentblock, and encodes or decodes the current block in the current picture.

In some embodiments, the video processing method in a video encoding ordecoding system comprises receiving input video data of a currenttransform block in a current picture, signaling or parsing a firstsyntax element in a high-level syntax set referred to by the currentpicture to derive first information for indicating whether a transformskip mode is enabled for transform blocks in an associated video datastructure referring to the high-level syntax set, signaling or parsing asecond syntax element in the high-level syntax set when the firstinformation indicates the transform skip mode is enabled for thetransform blocks in the associated video data structure, determiningwhether the transform skip mode is applied to the current transformblock when the first information indicates the transform skip mode isenabled, processing residues of the current transform block according tothe transform skip mode when the transform skip mode is applied to thecurrent transform block or processing residues of the current transformblock by a regular transform operation or a regular inverse transformoperation when the transform skip mode is not applied to the currenttransform block, and encoding or decoding the current transform block inthe current picture. The second syntax element is related to a minimumallowed Quantization Parameter (QP) value associated with quantizationof residues of the transform blocks coded using the transform skip mode.A QP value used for quantization of the residues of the currenttransform block is larger than or equal to the minimum allowed QP valuewhen the transform skip mode is applied to the current transform block.Some embodiments of the high-level syntax set include one or acombination of a SPS, PPS, picture header, and slice header. In oneembodiment, the video processing method further signals or parses asyntax element associated with a size constraint for enabling thetransform skip mode in the high-level syntax set when the first syntaxelement indicates the transform skip mode is enabled, and determines thesize constraint for enabling the transform skip mode according to thesyntax element associated with the size constraint for enabling thetransform skip mode. The step of determining whether the transform skipmode is applied to the current transform block in the current picture isperformed only when the current transform block satisfies the sizeconstraint for enabling the transform skip mode.

Other aspects and features of the invention will become apparent tothose with ordinary skill in the art upon review of the followingdescriptions of specific embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of this disclosure that are proposed as exampleswill be described in detail with reference to the following figures,wherein like numerals reference like elements, and wherein:

FIG. 1 illustrates an exemplary coding tree for splitting a Coding TreeUnit (CTU) into Coding Units (CUs) and splitting each CU into one ormore Transform Units (TUs) according to a quadtree splitting structure.

FIG. 2 illustrates a corresponding quadtree representation for the blockpartitioning structure as shown in FIG. 1.

FIG. 3 is a flowchart illustrating an embodiment of the video processingmethod for encoding a current block in a current picture by signaling asyntax element associated with a size constraint for enabling thetransform skip mode in a SPS only when the transform skip mode isenabled for the current picture.

FIG. 4 is a flowchart illustrating an embodiment of the video processingmethod for decoding a current picture by parsing a syntax elementassociated with a size constraint for enabling the transform skip modein a SPS only when the transform skip mode is enabled for the currentpicture.

FIG. 5 illustrates an exemplary system block diagram for a videoencoding system incorporating the video processing method according toembodiments of the present invention.

FIG. 6 illustrates an exemplary system block diagram for a videodecoding system incorporating the video processing method according toembodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

It will be readily understood that the components of the presentinvention, as generally described and illustrated in the figures herein,may be arranged and designed in a wide variety of differentconfigurations. Thus, the following more detailed description of theembodiments of the systems and methods of the present invention, asrepresented in the figures, is not intended to limit the scope of theinvention, as claimed, but is merely representative of selectedembodiments of the invention.

Reference throughout this specification to “an embodiment”, “someembodiments”, or similar language means that a particular feature,structure, or characteristic described in connection with theembodiments may be included in at least one embodiment of the presentinvention. Thus, appearances of the phrases “in an embodiment” or “insome embodiments” in various places throughout this specification arenot necessarily all referring to the same embodiment, these embodimentscan be implemented individually or in conjunction with one or more otherembodiments. Furthermore, the described features, structures, orcharacteristics may be combined in any suitable manner in one or moreembodiments. One skilled in the relevant art will recognize, however,that the invention can be practiced without one or more of the specificdetails, or with other methods, components, etc. In other instances,well-known structures, or operations are not shown or described indetail to avoid obscuring aspects of the invention.

The Joint Video Experts Team (JVET) of ITU-T SG16 WP3 and ISO/IECJTC1/SC29/WG11 is currently in the process of establishing thenext-generation video coding standard Versatile Video Coding (VVC). Somepromising new coding tools have been adopted into the VVC standard, andin the VVC draft specification, a coded picture is partitioned intonon-overlapped square block regions represented by CTUs, similar to theHEVC standard. Each CTU is partitioned into one or multiple smaller sizeCU by a quadtree with nested multi-type tree using binary and ternarysplit. The resulting CU partitions can be in square or rectangularshapes. The Transform Skip (TS) mode can be enabled by setting aSequence Parameter Set (SPS) level enabling flagsps_transform_skip_enabled_flag in the SPS equal to 1, and a maximumallowed block size for enabling the TS mode is signaled by a syntaxelement log 2_max_transform_skip_block_size_minus2 in a PictureParameter Set (PPS). Embodiments of the present invention improve codingefficiency and flexibility for implementing the transform skip mode in avideo coding system.

Separate Transform Skip Mode Control for Chroma

In accordance with one aspect of the present invention, a video codersignals or parses one or more High-Level Syntax (HLS) elements forcontrolling the use of the TS mode for chroma transform blocksseparately, in addition to the HLS elements associated with the lumatransform blocks. In this way, a video encoder or decoder can moreeffectively control the use of the TS mode for different colorcomponents with different statistical characteristics.

In one embodiment, a video coder encodes or decodes first informationfor indicating whether the TS mode is enabled for luma transform blocksin a video data structure using one or more first syntax elements in therelated high-level syntax structure such as the SPS, PPS, pictureheader, and slice header. The video coder further encodes or decodessecond information for indicating whether the TS mode is enabled forchroma transform blocks in the video data structure using one or moresecond syntax elements in the related high-level syntax structure. Insome embodiments of the present invention, the use of the TS mode can becontrolled independently for the luma and chroma components. In onespecific embodiment, the video coder is modified to signal two enablingflags sps_transform_skip_luma_enabled_flag andsps_transform_skip_chroma_enabled_flag in a SPS to indicate whether theTS mode is enabled for luma transform blocks and chroma transformblocks, respectively, in the coded video sequence that refers to theSPS. An exemplary high-level syntax table demonstrating an embodiment ofthe present invention is shown in Table 1, where ChromaArrayType!=0indicates the number of the color components is more than 1 in the codedsequence that refers to the SPS. The TS mode is disabled for lumatransform blocks or chroma transform blocks in the coded video sequencethat refers to the SPS when the corresponding syntax elementsps_transform_skip_luma_enabled_flag orsps_transform_skip_chroma_enabled_flag is equal to 0. The TS mode isenabled for luma transform blocks or chroma transform blocks in thecoded video sequence that refers to the SPS when the correspondingsyntax element sps_transform_skip_luma_enabled_flag orsps_transform_skip_chroma_enabled_flag is equal to 1.

TABLE 1 Descriptor seq_parameter_set_rbsp( ) {sps_decoding_parameter_set_id u(4) sps_video_parameter_set_id u(4) .....sps_transform_skip_luma_enabled_flag u(1) if( ChromaArrayType != 0 )sps_transform_skip_chroma_enabled_flag u(1) .... }

In some other embodiments, the use of the TS mode for the chromacomponents may be dependent on the use of the TS mode for the lumacomponent in a video coding system. An embodiment of a video encoder ordecoder infers that the TS mode for the chroma components is disabledwhen the TS mode is disabled for the luma component. For example, thevideo decoder disables the TS mode for a luma transform block afterparsing a TS mode luma enabling flag which is equal to 0, and the videodecoder also infers the TS mode for the corresponding chroma transformblocks is disabled when this TS mode luma enabling flag is equal to 0.In one specific embodiment, the video coder is modified to signal afirst syntax flag sps_transform_skip_enabled_flag in a SPS to indicatewhether the TS mode is enabled for luma transform blocks in the codedvideo sequence that refers to the SPS. When this SPS level TS enablingflag sps_transform_skip_enabled_flag is equal to 0, the TS mode isdisabled for luma transform blocks in the coded video sequence thatrefers to the SPS. When this SPS level TS enabling flagsps_transform_skip_enabled_flag is equal to 1, the TS mode is enabledfor luma transform blocks in the coded video sequence that refers to theSPS and the video coder further signals a second syntax flagsps_transform_skip_chroma_enabled_flag in the SPS to indicate whetherthe TS mode is enabled for chroma transform blocks. An exemplaryhigh-level syntax table is shown in Table 2 demonstrates the controllingof the TS mode for the chroma components is depending on the controllingof the TS mode for the luma component. The syntax elementsps_transform_skip_chroma_enabled_flag is inferred to be equal to 0 whenthis syntax element is not signaled, so that the TS mode is inferred tobe disabled for the chroma transform blocks.

TABLE 2 Descriptor seq_parameter_set_rbsp( ) {sps_decoding_parameter_set_id u(4) sps_video_parameter_set_id u(4) .....sps_transform_skip_enabled_flag u(1) if( sps_transform_skip_enabled_flag&& ChromaArrayType != 0 ) sps_transform_skip_chroma_enabled_flag u(1).... }

Transform Skip Mode Size Constraint Signaling

In some embodiments, the video encoders or decoders signal informationassociated with a size constraint for enabling the TS mode using one ormore syntax elements in one or more high-level syntax sets such as theSPS, PPS, picture header, and slice header when the TS mode is signaledto be enabled for transform blocks in a video data structure. Thehigh-level syntax set is also referred to as a high-level parameter set.In one specific embodiment, information associated with a TS mode sizeconstraint is signaled in or parsed from a SPS when a transform skipenabling flag signaled in or parsed from a high-level syntax set isequal to 1 indicating the TS mode is enabled. The high-level syntax setis one or a combination of a SPS, PPS, picture header, or slice header.For example, the transform skip enabling flag is signaled in the SPS. Insome embodiments of the present invention, the size constraint forenabling the TS mode is related to information for deriving a maximumallowed block size for enabling the TS mode. In some other embodiments,information for deriving a maximum allowed block size for enabling theTS mode is signaled using one or more high-level syntax elements in theSPS, PPS, picture header, or slice header. The specified block sizeconstraint may relate to the number of total pixel samples, width, orheight of a block. In some embodiments, the maximum allowed block sizefor enabling the TS mode for TBs shall be less than or equal to amaximum allowed transform block size or a maximum allowed non-emptytransform block size after zero-out TB for coding the TBs using theregular transform operation. In some embodiments, the maximum allowedblock size for enabling the TS mode for chroma TBs shall be less than orequal to a maximum allowed transform block size or a maximum allowednon-empty transform block size after zero-out TB for coding the chromaTBs using the regular transform operation.

In some embodiments of the present invention, when the SPS levelenabling flag sps_transform_skip_enabled_flag is equal to 1, the maximumallowed block size for enabling the TS mode is signaled by a syntaxelement log 2 max transform skip block size minus2 in the SPS. A syntaxelement sps_bdpcm_enabled_flag is further signaled to indicate whetherthe Block-based Delta Pulse Code Modulation (BDPCM) is enabled in theCoded Layered Video Sequence (CLVS) referring to the SPS. In oneembodiment, two coding processes are supported for coding residualblocks in the TS mode when the value of the associated syntax elementtransform_skip_flag equal to 1. In cases when a syntax elementslice_ts_residual_coding_disabled_flag in a slice header is equal to 0,a transform skip residual coding process with a syntax table specifiedby residual_ts_coding( ) is employed for coding residual blocks in theTS mode in the current slice. Otherwise when the syntax elementslice_ts_residual_coding_disabled_flag is equal to 1, a regular residualcoding process with a syntax table specified by residual_coding( ) isemployed for coding residual blocks in the TS mode in the current slice.

In some embodiments, a size constraint for enabling the TS mode forchroma TBs is derived from a related size constraint for luma TBssignaled by one or more HLS elements. In a specific embodiment, a videoencoder or decoder is modified to signal a syntax element sps_log2_transform_skip_max_size_minus2 in a SPS when the SPS level TS enablingflag sps_transform_skip_enabled_flag is equal to 1. The maximum allowedblock size in luma samples for enabling the TS mode for luma TBs isderived by (1<<(sps_log 2_transform_skip_max_size_minus2+2)). In oneembodiment, the maximum allowed block size in chroma samples forenabling the TS mode for chroma TBs is set equal to the same value asthat of for the luma TBs. In another embodiment, the maximum allowedblock size in chroma samples for enabling the TS mode for chroma TBs isset equal to (1<<(sps_log 2_transform_skip_max_size_minus2+2))/SubWidthCfor the block width and equal to (1<<(sps_log2_transform_skip_max_size_minus2+2))/SubHeightC for the block height.The variables SubWidthC and SubHeightC indicate down-sampling ratiosassociated with the chroma bitplanes in horizontal and verticaldimensions, respectively. In another embodiment, the maximum allowedblock size in chroma samples for enabling the TS mode for chroma TBs isset equal to a minimum of (1<(sps_log2_transform_skip_max_size_minus2+2), 32/SubWidthC) for the block widthand equal to a minimum of (1<<sps_log2_transform_skip_max_size_minus2+2), 32/SubHeightC) for the blockheight. In yet another embodiment, the maximum allowed block size inluma samples for enabling the TS mode for chroma TBs is derived by(1<<(sps_log 2_transform_skip_max_size_minus2+2)). Table 3 and Table 4provide exemplary syntax tables modified from Table 1 and Table 2,respectively, to further signal the maximum block size constraints forenabling the TS mode.

TABLE 3 Descriptor seq_parameter_set_rbsp( ) {sps_decoding_parameter_set_id u(4) sps_video_parameter_set_id u(4) .....sps_transform_skip_luma_enabled_flag u(1) if( ChromaArrayType != 0 )sps_transform_skip_chroma_enabled_flag u(1) if(sps_transform_skip_luma_enabled_flag ||sps_transform_skip_chroma_enabled_flag )sps_log2_transform_skip_max_size_minus2 ue(v) .... }

TABLE 4 Descriptor seq_parameter_set_rbsp( ) {sps_decoding_parameter_set_id u(4) sps_video_parameter_set_id u(4) .....sps_transform_skip_enabled_flag u(1) if( sps_transform_skip_enabled_flag) { if( ChromaArrayType != 0 ) sps_transform_skip_chroma_enabled_flagu(1) sps_log2_transform_skip_max_size_minus2 ue(v) } .... }

In some embodiments, the size constraint for enabling the TS mode isrespectively signaled for luma and chroma components using one or moreseparate HLS elements. Table 5 demonstrates an exemplary syntax tablemodified from Table 1 to further signal the maximum block sizeconstraints for the luma and chroma components, respectively. Themaximum allowed block size for enabling the TS mode for the lumacomponent is derived by (1<<(sps_log2_transform_skip_max_size_luma_minus2+2)) and the maximum allowed blocksize for enabling the TS mode for the chroma components is derived by(1<<(sps_log 2_transform_skip_max_size_chroma_minus2+2)).

TABLE 5 Descriptor seq_parameter_set_rbsp( ) {sps_decoding_parameter_set_id u(4) sps_video_parameter_set_id u(4) .....sps_transform_skip_luma_enabled_flag u(1) if(sps_transform_skip_luma_enabled_flag )sps_log2_transform_skip_max_size_luma_minus2 ue(v) if( ChromaArrayType!= 0 ) { sps_transform_skip_chroma_enabled_flag u(1) if(sps_transform_skip_chroma_enabled_flag )sps_log2_transform_skip_max_size_chroma_minus2 ue(v) } .... }

Minimum Quantization Parameter for Transform Skip Mode

In some embodiments, a video encoder or decoder encodes or decodes firstinformation for indicating whether the TS mode is enabled for transformblocks in an associated video data structure using one or more firstsyntax elements in one or more high-level syntax sets. The high-levelsyntax set is also referred to as a high-level parameter set. Someexamples of the high-level syntax sets are SPS, PPS, picture header, andslice header. In cases when the first information indicates the TS modeis enabled for the transform blocks in the associated video datastructure, the video encoder encodes second information related to aminimum allowed Quantization Parameter (QP) value associated withquantization of residues of the transform blocks in the TS mode bysignaling one or more second syntax elements in the high-level syntaxsets. Similarly, the video decoder decodes second information related toa minimum allowed QP value associated with inverse quantization of aquantized residual signal of the transform blocks in the TS mode byparsing one or more second syntax elements from the high-level syntaxsets.

In one specific embodiment, the video encoder or decoder is modified tosignal a first syntax flag sps_transform_skip_enabled_flag in a SPS toindicate whether the TS mode is enabled for transform blocks in thecoded video sequence that refers to the SPS. In cases when the firstsyntax flag sps_transform_skip_enabled_flag is equal to 0, the TS modeis disabled for transform blocks in the coded video sequence that refersto the SPS. In cases when the first syntax flagsps_transform_skip_enabled_flag is equal to 1, the TS mode is enabledfor transform blocks in the coded video sequence that refers to the SPSand the video coder further signals a second syntax element (forexample, min_qp_prime_ts_minus4) in the SPS for derivation of theminimum allowed quantization parameter for the TS mode. An exemplaryhigh-level syntax table of this embodiment is demonstrated in Table 6.

TABLE 6 Descriptor seq_parameter_set_rbsp( ) {sps_decoding_parameter_set_id u(4) sps_video_parameter_set_id u(4) .....sps_transform_skip_enabled_flag u(1) if( sps_transform_skip_enabled_flag) { min_qp_prime_ts_minus4 ue(v) .... }

Multiple Level Control for Transform Skip Mode

Various modified methods for signaling information at multiple levelsrelated to coding residual blocks in the TS mode in an image or videocoding system are disclosed. In one embodiment, when the TS mode isenabled in a high-level syntax set, one or more syntax elements can befurther signaled in the high-level syntax set to control whether one ormore syntax elements related to the TS mode shall be present in alower-level syntax set associated with each of lower-level video dataunits referring to the high-level syntax set. The video encoder ordecoder of this embodiment encodes or decodes a first syntax flag in ahigh-level syntax set to indicate whether the TS mode may be enabled forcoding a high-level video data unit. The video encoder or decoderfurther encodes or decodes a second syntax flag in the high-level syntaxset, and according to the second syntax flag, the video encoder ordecoder adaptively encodes or decodes one or more syntax elements in alower-level syntax set related to the TS mode for coding the associatedlower-level video data units. When the value of the first flag indicatesthat the TS mode may be enabled for coding the high-level video dataunits, the video encoder or decoder further encodes or decodes thesecond syntax flag in the high-level syntax set. The video encoder ordecoder encodes or decodes one or more syntax elements in thelower-level syntax set when the second syntax flag indicates the one ormore syntax elements are present in the lower-level syntax set. Forexample, the high-level syntax set can be the SPS that applies to zeroor more entire CLVSs or the PPS that applies to zero or more entirecoded pictures, or the picture header that applied to all coded slicesof a current picture in the VVC standard. The lower-level syntax set canbe the picture header associated with the current coded picture or theslice header associated with the current coded slice in the VVCstandard. The one or more syntax elements in the lower-level syntax setare set to a default setting when the one or more syntax elements arenot signaled. In some embodiments, the default setting is derived by apredefined method. An example of the predefined method deriving thedefault setting from the related parameters in the high-level syntax setthat is referred to by the current lower-level syntax set. In anotherexample, the default setting is explicitly signaled by one or moresyntax elements in the high-level syntax set that is referred to by thecurrent lower-level syntax set. In this way, when a video encoder ordecoder determines to adopt a fixed setting for luma mapping with chromascaling for a high-level video data unit such as a CLVS, it can signal asecond syntax flag in a high-level syntax set such as the SPS toindicate that the syntax information related to adaptively controllingthe use of luma mapping with chroma scaling is skipped in a lower-levelsyntax set for each of lower-level video data units referring to thehigh-level syntax set.

A video encoder or decoder is modified according to another embodimentto signal or parse a new syntax elementsps_ts_residual_coding_disabled_slice_present_flag in a SPS when a SPSlevel enabling flag sps_transform_skip_enabled_flag signaled in orparsed from the SPS is equal to 1. When this new syntax elementsps_ts_residual_coding_disabled_slice_present_flag is equal to 1, aslice level syntax element slice_ts_residual_coding_disabled_flag ispresent in slice headers referring to the SPS through the referred PPS.When this new syntax elementsps_ts_residual_coding_disabled_slice_present_flag is equal to 0, theslice level syntax element slice_ts_residual_coding_disabled_flag isinferred to be equal to 0 and is not present in slice headers referringto the SPS. The modified syntax tables for the SPS and slice headeraccording to this embodiment are provided in Table 7 and Table 8respectively.

TABLE 7 Descriptor seq_parameter_set_rbsp( ) { sps_seq_parameter_set_idu(4) sps_video_parameter_set_id u(4)  .....sps_transform_skip_enabled_flag u(1) if( sps_transform_skip_enabled_flag) {  log2_transform_skip_max_size_minus2 ue(v)  sps_bdpcm_enabled_flagu(1) sps_ts_residual_coding_disabled_slice_present_flag u(1)  }  .... }

TABLE 8 Descriptor slice_header( ) { picture_header_in_slice_header_flagu(1) ..... if( sps_ts_residual_coding_disabled_slice_present_flag )slice_ts_residual_coding_disabled_flag u(1) .... }

The related semantics for the syntax elementssps_ts_residual_coding_disabled_slice_present_flag andslice_ts_residual_coding_disabled_flag are shown in the following. Thesyntax element sps_ts_residual_coding_disabled_slice_present_flag equalsto 1 specifying that the syntax elementslice_ts_residual_coding_disabled_flag is present in the slice headersreferring to the SPS. The syntax elementsps_ts_residual_coding_disabled_slice_present_flag equals to 0specifying that the syntax elementslice_ts_residual_coding_disabled_flag is not present in the sliceheaders referring to the SPS. When this syntax elementsps_ts_residual_coding_disabled_slice_present_flag is not present, it isinferred to be equal to 0. The syntax elementslice_ts_residual_coding_disabled_flag equals to 1 specifying that thesyntax structure residual_coding is used to parse the residual samplesof a transform skip block for the current slice. The syntax elementslice_ts_residual_coding_disabled_flag equals to 0 specifying that thesyntax structure residual_ts_coding( ) is used to parse the residualsamples of a transform skip block for the current slice. When thissyntax element slice_ts_residual_coding_disabled_flag is not present, itis inferred to be equal to 0. The syntax structure residual_coding( )parses the residual samples by the regular residual coding process whilethe syntax structure residual_ts_coding( ) parses the residual samplesby the transform skip residual coding process.

In an alternative embodiment, when the syntax elementsps_ts_residual_coding_disabled_slice_present_flag is equal to 0, a newsyntax element sps_ts_residual_coding_disabled_slice_default_flag isfurther signaled in the SPS. When the syntax elementslice_ts_residual_coding_disabled_flag is not present in the sliceheaders referring to the SPS, it is inferred to be equal to the value ofthe new syntax elementsps_ts_residual_coding_disabled_slice_default_flag.

TABLE 9 Descriptor seq_parameter_set_rbsp( ) { sps_seq_parameter_set_idu(4) sps_video_parameter_set_id u(4) .....sps_transform_skip_enabled_flag u(1) if( sps_transform_skip_enabled_flag) { log2_transform_skip_max_size_minus2 ue(v) sps_bdpcm_enabled_flagu(1) sps_ts_residual_coding_disabled_slice_present_flag u(1) if (!sps_ts_residual_coding_disabled_slice_present_flag)sps_ts_residual_coding_disabled_slice_default_flag u(1) } .... }

TABLE 10 Descriptor slice_header( ) {picture_header_in_slice_header_flag u(1) ..... if(sps_ts_residual_coding_disabled_slice_present_flag )slice_ts_residual_coding_disabled_flag u(1) .... }

The related semantics for some of the syntax elements signaled in theSPS as shown in Table 9 are illustrated in the following. The syntaxelement sps_ts_residual_coding_disabled_slice_present_flag equals to 1specifying that the syntax elementslice_ts_residual_coding_disabled_flag is present in slice headersreferring to the SPS. The syntax elementsps_ts_residual_coding_disabled_slice_present_flag equals to 0specifying that the syntax elementslice_ts_residual_coding_disabled_flag is not present in the sliceheaders referring to the SPS. This syntax element is inferred to beequal to 0 when it is not present. The syntax elementsps_ts_residual_coding_disabled_slice_default_flag specifies the defaultvalue for the syntax element slice_ts_residual_coding_disabled_flag whenthe syntax element sps_ts_residual_coding_disabled_sice_present_flag isequal to 0 for slice headers referring to the SPS.

The syntax element slice_ts_residual_coding_disabled_flag signaled inthe slice header of a current slice as shown in Table 10 equals to 1specifying that the syntax structure residual_coding is used to parsethe residual samples of a transform skip block for the current slice.The syntax element slice_ts_residual_coding_disabled_flag equals to 0specifying that the syntax structure residual_ts_coding( ) is used toparse the residual samples of a transform skip block for the currentslice. This syntax element slice_ts_residual_coding_disabled_flag isinferred to be equal to the value of the syntax elementsps_ts_residual_coding_disabled_slice_default_flag signaled in the SPSif the syntax element slice_ts_residual_coding_disabled_flag is notpresent in the slice header.

Adaptively Adjust Parametric Setting for Transform Skip Mode inLower-Level Video Data Structure

In accordance with another aspect of the present invention, a videocoder signals or parses one or more syntax elements in one or morelower-level syntax structures for adaptively adjusting the parametricsetting for controlling the use of the TS mode in lower-level video datastructures. The lower-level syntax structure is also referred to as alower-level syntax set. Some examples of the lower-level syntaxstructures are the PPS, picture header set, and slice header. In thisway, the use of the transform skip mode can be more effectivelycontrolled considering picture contents and coding conditions forencoding picture regions. In some embodiments of the present invention,a video encoder or decoder encodes or decodes one or more syntaxelements in a high-level syntax set for signaling information forderiving the parametric setting for controlling the use of the TS modein a high-level video data structure. The video coder further encodes ordecodes one or more syntax elements in one or more lower-level syntaxsets to indicate if the setting for controlling the use of the TS modesignaled in the high-level syntax set that is referred to by thelower-level syntax sets is to be reused or modified for encoding ordecoding associated lower-level video data structures. The video encoderor decoder further encodes or decodes one or more syntax elements in oneor more lower-level syntax sets for signaling information for derivingthe modified parametric setting for controlling the use of the TS modefor encoding or decoding the associated lower-level video datastructures. The video encoder or decoder may further encode or decode asyntax element in the high-level syntax structure to indicate if thesetting for controlling the use of the TS mode signaled in a high-levelsyntax set is allowed to be modified or replaced in a particularlower-level syntax structure that refers to the high-level syntax set.

In one embodiment, the video coder is modified to encode or decode asyntax element sps_pic_transform_skip_present_flag in a SPS when the TSmode is enabled for transform blocks in the coded video sequence thatrefers to the SPS. When this syntax elementsps_pic_transform_skip_present_flag is equal to 0 in the SPS, theparametric setting for the TS mode signaled in the SPS that is referredto by a current picture is applied to encode or decode the currentpicture. Otherwise, the parametric setting for the TS mode in thecurrent picture can be further modified. The video encoder or decoderfurther encodes or decodes a syntax elementpic_transform_skip_present_flag in a picture header of the currentpicture to indicate if the parametric setting for the TS mode signaledin the SPS that is referred to by the current picture is reused forencoding or decoding the current picture. The syntax elementpic_transform_skip_present_flag is referred to be equal to 0 when thissyntax element is not present. Exemplary syntax tables shown in Table 11and Table 12 illustrate an embodiment of supporting the modifiedparametric setting for controlling the use of the TS mode in alower-level video data structure. In this embodiment, the high-levelsyntax structure for signaling syntax elements associated with thecontrol of the parametric setting for the TS mode is a SPS and thelower-level syntax structure for signaling syntax elements associatedwith the control of the parametric setting for the TS mode is a pictureheader. The syntax element pic_transform_skip_enabled_flag signaled inthe picture header specifies if the TS mode can be enabled in thecurrent picture, and the syntax element pic_log2_transform_skip_max_size_minus2 signaled in the picture header plus 2specifies the maximum allowed transform block size for enabling the TSmode in the current picture. In cases when the syntax elementpic_transform_skip_present flag is equal to 0, the values of the syntaxelement pic_transform_skip_enabled_flag and pic_log2_transform_skip_max_size_minus2 are inferred to be equal to values ofassociated SPS level syntax elements sps_transform_skip_enabled_flag andsps_log 2_transform_skip_max_size_minus2, respectively. The associatedSPS level syntax elements are signaled in the SPS that is referred to bythe current picture header by referring to the PPS that refers to theSPS.

TABLE 11 Descriptor seq_parameter_set_rbsp( ) {sps_decoding_parameter_set_id u(4) sps_video_parameter_set_id u(4) .....sps_transform_skip_enabled_flag u(1) if( sps_transform_skip_enabled_flag) { sps_pic_transform_skip_present_flag u(1)sps_log2_transform_skip_max_size_minus2 ue(v) } .... }

TABLE 12 Descriptor picture_header _rbsp( ) { non_reference_picture_flagu(1) gdr_pic_flag u(1) no_output_of_prior_pics_flag u(1) if(gdr_pic_flag )  recovery_poc_cnt ue(v) ph_pic_parameter_set_id ue(v) ..... if( sps_pic_transform_skip_present_flag ) {pic_transform_skip_present_flag u(1) if (pic_transform_skip_present_flag ) {  pic_transform_skip_enabled_flagu(1)  if( pic_transform_skip_enabled_flag ) pic_log2_transform_skip_max_size_minus2 ue(v) }  }  .... }

Exemplary Flowcharts

FIG. 3 is a flowchart illustrating an exemplary embodiment of the videoprocessing method implemented in a video encoding system. The videoencoding system in this exemplary embodiment first receives input dataassociated with a current block in a current picture in step S302. Thevideo encoding system determines if the TS mode is enabled for thecurrent block in step S304. For example, an enabling flag is signaled ina high-level syntax set referred to by the current picture, and theenabling flag is set to 1 to indicate the TS mode is enabled for one ormore pictures associated with the high-level syntax set. The high-levelsyntax set may be one or a combination of a SPS, PPS, and picture headerreferred to by the current picture. The video encoding system signals asyntax element associated with a size constraint for enabling the TSmode in the SPS referred to by the current picture when the TS mode isenabled. The video encoding system checks if the current block satisfiesthe size constraint for enabling the TS mode in step S306, and only whenthe TS mode is enabled for the current block and the current blocksatisfies the size constraint, the video encoding system determineswhether the TS mode is applied to the current block in step S308.Residues of the current block are processed according to the TS mode instep S310 when the TS mode is applied to the current block; otherwise,residues of the current block are processed by a regular transformoperation in step S312 when the TS mode is not applied to the currentblock. The regular transform operation in step S312 is selected toprocess the residues of the current block when the TS mode is notenabled for the current block in step S304 or when the current blockdoes not satisfy the size constraint for enabling the TS mode in stepS306. The video encoding system encodes the current block in step S314.

FIG. 4 is a flowchart illustrating an exemplary embodiment of the videoprocessing method implemented in a video decoding system. The videodecoding system in this exemplary embodiment receives input video dataof a current picture in step S402, and obtains an enabling flag signaledin a high-level syntax set indicating whether a TS mode is enabled instep S404. The high-level syntax set may be one or a combination of aSPS, PPS, picture header, and slice header referred to by the currentpicture or associated to the current picture. In step S406, the videodecoding system determines if the TS mode is enabled according to theenabling flag obtained from step S404. The video decoding system furtherobtains a syntax element associated with a size constraint for enablingthe TS mode signaled in a SPS referred to by the current picture in stepS408 when the TS mode is enabled. The video decoding system receivesinput video data associated with a current block in step S410, andchecks whether the current block satisfies the size constraint forenabling the TS mode in step S412 when the TS mode is enabled for thecurrent picture. For example, the size constraint is related to amaximum allowed block size, and the TS mode can only be applied to thecurrent block when a size of the current block is smaller than or equalto the maximum allowed block size. In cases when the current blocksatisfies the size constraint, the video decoding system determines ifthe TS mode is applied to the current block in step S414. For example,the video decoding system determines if the TS mode is applied to thecurrent block according to a block-level syntax element. Residues of thecurrent block are recovered according to the TS mode in step S416 if theTS mode is applied to the current block; otherwise, residues of thecurrent block are recovered by a regular inverse transform operation instep S418 if the TS mode is not applied to the current block in stepS414 or when the current block does not satisfy the size constraint instep S412. The video decoding system decodes the current block in stepS420 and checks if the current block is a last block in the currentpicture in step S422. The video decoding system repeats the steps fromstep S410 to step S420 to process each subsequent block in the currentpicture if the current block is not the last block; otherwise the videodecoding system processes a subsequent picture referring to the samehigh-level syntax set. Residues of the current picture are recovered bya regular inverse transform operation and the current picture is decodedin step S424 when the TS mode is not enabled for coding the currentpicture in step S406.

Exemplary System Block Diagrams

Embodiments of the video processing method are implemented in videoencoders, video decoders, or both the video encoders and decoders. Forexample, the video processing method is implemented in a high-levelsyntax encoding module of the video encoder or in a high-level syntaxdecoding module of the video decoder. Alternatively, the videoprocessing method is implemented in a circuit integrated to thehigh-level syntax encoding module of the video encoder or the high-levelsyntax decoding module of the video decoder. FIG. 5 illustrates anexemplary system block diagram for a Video Encoder 500 implementingvarious embodiments of the video processing method. A Block StructurePartitioning module 510 receives input data of video pictures anddetermines a block partitioning structure for each video picture to beencoded. Each leaf coding block in the current video picture ispredicted by intra prediction in an Intra Prediction module 512 or byinter prediction in an Inter Prediction module 514 to remove spatialredundancy or temporal redundancy. The Intra Prediction module 512provides intra predictors for the leaf coding block based onreconstructed video data of the current video picture. The InterPrediction module 514 performs Motion Estimation (ME) and MotionCompensation (MC) to provide predictors for the leaf coding block basedon video data from other video picture or pictures. A Switch 516 selectseither the Intra Prediction module 512 or Inter Prediction module 514 tosupply the predictor to an Adder 518 to form prediction errors, alsocalled residues. The residues of each leaf coding block in the currentvideo picture are divided into multiple transform blocks. The residuesof each transform block are further processed by a Transform (T) module520 followed by a Quantization (Q) module 522 to generate transformcoefficient levels. In some embodiments of the present invention, theTransform Skip (TS) mode is enabled for the current video picture andthe TS mode may be used to process the residues of a current transformblock if the current transform block satisfies a size constraint. Whenthe TS mode is used to process the current transform block, residues ofthe current transform block are not transform into a frequency domain.In one embodiment, the size constraint for enabling the TS mode issignaled in a SPS for a current video sequence only when the TS mode isenabled for the current video sequence. That is the size constraint issignaled in the SPS when a SPS level TS enabling flag signaled in theSPS is equal to 1. In another embodiment, the presence of a syntaxelement for deriving a minimum allowed QP value for the TS mode isconditioned on the SPS level TS enabling flag signaled in the SPS,wherein the syntax element for deriving a minimum allowed QP value forthe TS mode is min_qp_prime_ts_minus4 or any other syntax element forderiving a minimum allowed QP value for the TS mode. The Entropy Encoder534 also encodes prediction information and filter information to form avideo bitstream. The video bitstream is then packed with sideinformation. The transform coefficient levels of the current transformblock are processed by an Inverse Quantization (IQ) module 524 and anInverse Transform (IT) module 526 to recover the residual data of thecurrent transform block. In cases when the TS mode is used to processthe current transform block, an inverse transform operation is alsoskipped. As shown in FIG. 5, reconstructed video data are recovered byadding back the residual data to the selected predictor at aReconstruction (REC) module 528. The reconstructed video data may bestored in a Reference Picture Buffer (Ref. Pict. Buffer) 532 and used byan Inter Prediction module 514 for prediction of other pictures. Thereconstructed video data from the Reconstruction module 528 may besubject to various impairments due to the encoding processing,consequently, an In-loop Processing Filter 530 is applied to thereconstructed video data before storing in the Reference Picture Buffer532 to further enhance picture quality.

A corresponding Video Decoder 600 for decoding the video bitstreamgenerated by the Video Encoder 500 of FIG. 5 is shown in FIG. 6. Theinput to the Video Decoder 600 is decoded by an Entropy Decoder 610 toparse and recover transform coefficient levels of each transform blockand other system information. In some embodiments, the Entropy Decoder610 first parses an enabling flag for the TS mode from a high-levelsyntax set such as a SPS, PPS, picture header, or slice header. TheEntropy Decoder 610 parses a syntax element associated with a sizeconstraint for enabling the TS mode from the SPS only if the enablingflag for the TS mode indicates the TS mode is enabled according to someembodiments of the present invention. In some embodiments, the EntropyDecoder 510 parses a syntax element from the high-level syntax set toderive a minimum allowed QP value for the TS mode if the enabling flagfor the TS mode indicates the TS mode is enabled, wherein the syntaxelement is min_qp_prime_ts_minus4 or any other syntax element forderiving a minimum allowed QP value for the TS mode. A Block StructurePartitioning module 612 determines a block partitioning structure ofeach block in each video picture. The decoding process of the Decoder600 is similar to the reconstruction loop at the Encoder 500, except theDecoder 600 only requires motion compensation prediction in an InterPrediction module 616. Each leaf block in the video picture is decodedby either an Intra Prediction module 614 or Inter Prediction module 616,and a Switch 618 selects an Intra predictor or Inter predictor accordingto decoded mode information. The transform coefficient levels associatedwith a current transform block are recovered by an Inverse Quantization(IQ) module 622 and an Inverse Transform (IT) module 624 when thecurrent transform block is not processed by the TS mode. The coefficientlevels associated with a current transform block are recovered by theInverse Quantization (IQ) module 622 when the current transform block isprocessed by the TS mode. The recovered residues are reconstructed byadding back the predictor in a Reconstruction (REC) module 620 toproduce reconstructed video. The reconstructed video is furtherprocessed by an In-loop Processing Filter (Filter) 626 to generate finaldecoded video. If a currently decoded video picture is a referencepicture, the reconstructed video of the currently decoded video pictureis also stored in a Reference Picture Buffer 628 for later pictures indecoding order.

Various components of the Video Encoder 500 and Video Decoder 600 inFIG. 5 and FIG. 6 may be implemented by hardware components, one or moreprocessors configured to execute program instructions stored in amemory, or a combination of hardware and processor. For example, aprocessor executes program instructions to control signaling or parsinga syntax element associated with a size constraint for enabling the TSmode when the TS mode is enabled. The processor is equipped with asingle or multiple processing cores. In some examples, the processorexecutes program instructions to perform functions in some components inthe Encoder 500 and Decoder 600, and the memory electrically coupledwith the processor is used to store the program instructions,information corresponding to the reconstructed data, and/or intermediatedata during the encoding or decoding process. The memory in someembodiments includes a non-transitory computer readable medium, such asa semiconductor or solid-state memory, a Random Access Memory (RAM), aRead-Only Memory (ROM), a hard disk, an optical disk, or other suitablestorage medium. The memory may also be a combination of two or more ofthe non-transitory computer readable mediums listed above. As shown inFIGS. 5 and 6, the Encoder 500 and Decoder 600 may be implemented in thesame electronic device, so various functional components of the Encoder500 and Decoder 600 may be shared or reused if implemented in the sameelectronic device. Any of the embodiments of the present invention maybe implemented in the Entropy Encoder 534 of the Encoder 500, and/or theEntropy Decoder 610 of the Decoder 600. Alternatively, any of theembodiments may be implemented as a circuit coupled to the EntropyEncoder 534 of the Encoder 500 and/or the Entropy Decoder 610 of theDecoder 600, so as to provide the information needed by the EntropyEncoder 534 or the Entropy Decoder 610 respectively.

Embodiments of the video processing methods with one or more partitionconstraints may be implemented in a circuit integrated into a videocompression chip or program code integrated into video compressionsoftware to perform the processing described above. For examples,determining of a block partitioning structure for the current block maybe realized in program codes to be executed on a computer processor, aDigital Signal Processor (DSP), a microprocessor, or Field ProgrammableGate Array (FPGA). These processors can be configured to performparticular tasks according to the invention, by executingmachine-readable software code or firmware code that defines theparticular methods embodied by the invention.

The invention may be embodied in other specific forms without departingfrom its spirit or essential characteristics. The described examples areto be considered in all respects only as illustrative and notrestrictive. The scope of the invention is therefore, indicated by theappended claims rather than by the foregoing description. All changeswhich come within the meaning and range of equivalency of the claims areto be embraced within their scope.

The invention claimed is:
 1. A video processing method in a videoencoding or decoding system, comprising: receiving input video data of acurrent block in a current picture; determining whether a transform skipmode is enabled for the current block; signaling a syntax elementassociated with a size constraint for enabling the transform skip modein a Sequence Parameter Set (SPS) referred to by the current picturewhen the transform skip mode is enabled or parsing a syntax elementassociated with a size constraint for enabling the transform skip modefrom a SPS referred to by the current picture when the transform skipmode is enabled; determining whether the transform skip mode is appliedto the current block in the current picture when the transform skip modeis enabled for the current block and the current block satisfies thesize constraint for enabling the transform skip mode; processingresidues associated with the current block according to the transformskip mode when the transform skip mode is applied to the current blockor processing residues of the current block by a regular transformoperation or regular inverse transform operation when the transform skipmode is not applied to the current block; and encoding or decoding thecurrent block in the current picture.
 2. The method of claim 1, whereinthe step of determining whether a transform skip mode is enabled for thecurrent block comprises parsing an enabling flag for the transform skipmode from a high-level syntax set, and the transform skip mode isenabled for the current block when the enabling flag is equal to
 1. 3.The method of claim 2, wherein the high-level syntax set comprises oneor a combination of the SPS, Picture Parameter Set (PPS), pictureheader, and slice header.
 4. The method of claim 2, further comprisingsignaling or parsing a new syntax element in the SPS when the enablingflag is equal to 1, wherein the new syntax element indicates whether aslice level syntax element is present in slice headers referring to theSPS, and the slice level syntax element for a current slice is used todetermine parsing residues of transform skip blocks in the current sliceby a regular residual coding process or transform skip residual codingprocess.
 5. The method of claim 1, further comprising signalinginformation related to a minimum allowed Quantization Parameter (QP)value associated with quantization of residues of transform blocksprocessed using the transform skip mode in the SPS when the transformskip mode is enabled for the current picture or parsing informationrelated to a minimum allowed QP value associated with inversequantization of a quantized residual signal of transform blocksprocessed using the transform skip mode from the SPS when the transformskip mode is enabled for the current picture.
 6. The method of claim 1,wherein the syntax element associated with a size constraint forenabling the transform skip mode corresponds to information for derivinga maximum allowed block size for enabling the transform skip mode. 7.The method of claim 6, wherein the maximum allowed block size forenabling the transform skip mode relates to a number of total pixelsamples, a width, or a height of a block.
 8. The method of claim 6,wherein the maximum allowed block size for enabling the transform skipmode is less than or equal to a maximum allowed transform block size ora maximum allowed non-empty transform block size for coding transformblocks using the regular transform operation.
 9. The method of claim 6,wherein the maximum allowed block size for enabling the transform skipmode for chroma transform blocks is less than or equal to a maximumallowed transform block size or a maximum allowed non-empty transformblock size for coding the chroma transform blocks using the regulartransform operation.
 10. The method of claim 1, wherein the syntaxelement associated with a size constraint for the transform skip modesignaled in the SPS is for luma transform blocks, and a size constraintfor enabling the transform skip mode for chroma transform blocks isderived from the size constraint for enabling the transform skip modefor the luma transform blocks.
 11. The method of claim 10, wherein thesize constraint for enabling the transform skip mode for the chromatransform blocks is set equal to a same value as the size constraint forenabling the transform skip mode for the luma transform blocks.
 12. Themethod of claim 10, wherein the size constraint for enabling thetransform skip mode for the chroma transform blocks is derived accordingto the size constraint for enabling the transform skip mode for the lumatransform blocks and variables indicating down-sampling ratiosassociated with chroma bitplanes in horizontal and vertical dimensions.13. The method of claim 1, further comprising signaling a second syntaxflag in a high-level syntax set or parsing a second syntax flag from ahigh-level syntax set when the transform skip mode is enabled for thecurrent block, wherein the second syntax flag is used to control whetherone or more syntax elements related to the transform skip mode arepresent in a lower-level syntax set associated with each of lower-levelvideo data units referring to the high-level syntax set.
 14. The methodof claim 13, wherein the high-level syntax set is the SPS, a PictureParameter Set (PPS) referred to by the current picture, or a pictureheader associated with the current picture, and the lower-level syntaxset is a picture header associated with the current picture or a sliceheader associated with a current slice in the current picture.
 15. Themethod of claim 13, wherein the one or more syntax elements related tothe transform skip mode are set to a default setting when the one ormore syntax elements are not signaled in the lower-level syntax set. 16.The method of claim 15, wherein the default setting is derived fromrelated parameters signaled in the high-level syntax set or the defaultsetting is explicitly signaled by one or more syntax elements in thehigh-level syntax set.
 17. An apparatus of processing video data in avideo encoding or decoding system, the apparatus comprising one or moreelectronic circuits configured for: receiving input video data of acurrent block in a current picture; determining whether a transform skipmode is enabled for the current block; signaling a syntax elementassociated with a size constraint for enabling the transform skip modein a Sequence Parameter Set (SPS) referred to by the current picturewhen the transform skip mode is enabled or parsing a syntax elementassociated with a size constraint for enabling the transform skip modefrom a SPS referred to by the current picture when the transform skipmode is enabled; determining whether the transform skip mode is appliedto the current block in the current picture when the transform skip modeis enabled for the current block and the current block satisfies thesize constraint for enabling the transform skip mode; processingresidues associated with the current block according to the transformskip mode when the transform skip mode is applied to the current blockor processing residues of the current block by a regular transformoperation or regular inverse transform operation when the transform skipmode is not applied to the current block; and encoding or decoding thecurrent block in the current picture.